Channel-assignment for a multi-channel dual-radio mesh backhaul

ABSTRACT

In an example embodiment, a method for determining backhaul channel assignments for multi-channel dual radio mesh nodes. The method comprises acquiring collision domain data for each access point of an associated mesh network. A cost function is calculated for each access point of the associated mesh network, the cost function assigning a weighted value for each access point in a collision domain based on a number of access points in the collision domain. Backhaul channel assignments for selected for each access point that minimizes the cost function.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/931,950, filed Oct. 31, 2007 now U.S. Pat. No. 7,849,216.

TECHNICAL FIELD

This application is generally directed to Mesh Networking.

BACKGROUND

In a multi-hop wireless mesh network, throughput decreases approximatelybetween linearly and exponentially with an increase in hop count, due tointerference generated by neighboring mesh Access Points (MAPs) on thesame channel. The end-to-end throughput available to each node in thesame network can be represented by

${O\left( \frac{1}{\sqrt{n}} \right)},$where n is the number of nodes in the network. Further, due tocontention from subsequent forwarding nodes, the end-to-end throughputthat a daisy-chained network can achieve is approximately 1/7 of theavailable capacity.

Unlike cellular networks or Wireless Local Area Networks (WLANs),wireless mesh networks have unique characteristics, such asself-healing, self-forming, multi-hop forwarding, and trafficaggregation at every downstream Access Point (AP). Existing solutionsoften assume a flat mesh topology and assign channels dynamically in adistributed fashion over a short period of time, incurring large channelswitching overhead and high complexity. Some vendors have multi-radioand multi-channel backhaul products; however, a static channelassignment algorithm is often utilized, where channels are determinedwhen the network is setup and manually configured at each mesh AP.

OVERVIEW OF EXAMPLE EMBODIMENTS

The following presents a simplified overview of the example embodimentsin order to provide a basic understanding of some aspects of the exampleembodiments. This overview is not an extensive overview of the exampleembodiments. Its sole purpose is to present some concepts of the exampleembodiments in a simplified form as a prelude to the more detaileddescription that is presented later.

In accordance with an example embodiment, there is disclosed herein, anapparatus comprising a transceiver configured to be in datacommunication with an associated mesh network and channel assignmentlogic in data communication with the transceiver. The channel assignmentlogic is operable to assign backhaul channels to each access point ofthe associated mesh network. The channel assignment acquires collisiondomain data for each access point of the associated mesh network andassigns a backhaul channel to each access point of the associated meshnetwork in order to minimize a maximum number of weighted nodes sharingthe channel within a collision domain.

In an example embodiment, a method for determining backhaul channelassignments for multi-channel dual radio mesh nodes. The methodcomprises acquiring collision domain data for each access point of anassociated mesh network. A cost function is calculated for each accesspoint of the associated mesh network, the cost function assigning aweighted value for each access point in a collision domain based on anumber of access points in the collision domain. Backhaul channelassignments for selected for each access point that minimizes the costfunction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example embodiment of an apparatus configured toperform channel assignment for a multi-channel dual-radio mesh backhaul.

FIG. 2 is an example of a mesh network employing a controller to performchannel assignment for a multi-channel dual-radio mesh backhaul.

FIG. 3 illustrates a computer system configured to implement an exampleembodiment.

FIG. 4 illustrates an example methodology for performing channelassignment for a multi-channel dual-radio mesh backhaul.

DESCRIPTION OF EXAMPLE EMBODIMENTS

This description provides examples not intended to limit the scope ofthe claims. The figures generally indicate the features of the examples,where it is understood and appreciated that like reference numerals areused to refer to like elements.

Described in an example embodiment herein is a dynamic channelassignment scheme that considers traffic load, network topology, andinterference. Further, an example embodiment described herein utilizesthe controller architecture and allows controller to make a centralizeddecision based on information gathered at each mesh AP.

Many channel assignment problems can be formulated as graph coloringproblems with different constraints. A wireless mesh network can beformulated as an undirected graph G={V, E}, where V represents the setof mesh nodes and E is the set of edges that represent radio links. Ifthe number of available channels, denoted by |C|, is sufficiently large,the channel assignment algorithm should assign distinct channels to anynodes within any collision domain. However, in many cases, depending onthe Signal-to-Interference Ratio (SIR) required at the receivers of thebackhaul nodes, the number of available channels may be less than thenumber of nodes in a collision domain and channels have to be carefullyassigned to mesh nodes to avoid conflicts as much as possible. Intwo-radio backhaul systems, all children nodes of the same parent areassigned the same channel.

In a wireless ad hoc network, it is desirable to minimize the number ofnodes sharing the same channel with any designated node within thisnode's collision domain. A collision domain is defined as a node's(k+1)-hop neighborhood, where k is the ratio between the carrier senserange and the communication range. The carrier sense range can beapproximately determined by the transmit power, the pathloss, and thereceiver sensitivity at the lowest data rate, whereas the communicationrange is determined by the transmit power, the pathloss, and thereceiver sensitivity at the desired data rate. For example, a 24 Mbps or18 Mbps mesh backhaul operating in a suburban environment, k isapproximately 2. Another way to determine the collision domain is toutilize the measurements reported from mesh APs because the RFenvironment surrounding each AP may be different.

In an example embodiment, to determine each mesh AP's collision domainempirically, 11 k/RRM (Radio Resource Management) exchanges may be usedby each mesh node to determine signal strength from all its peers. Thisdata can be shared or sent up to the controller to allow the collisiondomains to be predicted.

In another example embodiment, the following procedure could be used. Alink test is run on any individual link and the maximum throughput isrecorded. Then, simultaneous traffic flows are sent on any two links,and the maximum throughput on each link is measured. If the sum of theindividual throughput on two links and the combined throughput measuredwhen both links are tested are similar, the two links are not in thesame collision domain. Otherwise, the two links are in the samecollision domain.

Unlike ad hoc networks that have relative flat topologies, a wirelessmesh network has a tree-like topology and traffic aggregates towards theroot of the tree. Thus, different constrains and cost functions areneeded. In the example embodiments described herein, assume that eachnode has two backhaul radios although the same approach can be appliedto other configurations

In an example embodiment, given the characteristics of mesh networks,two additional constraints for channel assignment are employed:

-   -   1) Because each node is equipped with two backhaul radios, each        node is assigned two unique channels: one is used for the        upstream communication with its parent node and the other is        used for downstream communication with its children. All        children of the same parent share the same upstream channel to        avoid the channel switching overhead at the parent node.    -   2) Traffic aggregates in mesh networks. The closer a node is to        the root AP (RAP), the heavier the traffic becomes. Thus, the        nodes with lower hop counts are given higher priority than the        nodes with higher hop counts when getting channels.        In an example embodiment described herein, a goal is to minimize        the maximum number of weighted nodes sharing the same channel        within the same collision domain, for example:

${{Minimize}\mspace{14mu}{over}\mspace{14mu} c_{j}} \in {C\text{:}\mspace{20mu}\max\;{\sum\limits_{i = 1}^{\;_{N_{j}}}\; w_{i}}}$to where N_(j) is the number of nodes in the same collision domain thatutilize the same channel c_(j)εC communicate with its parent. w_(i) isthe weight assigned to the ith node and it is calculated as the count ofthe number of nodes on the subtree rooted at the ith node. w_(i) is alsodefined to take the traffic aggregation factor into consideration.

In an example embodiment, to ensure fast routing convergence at initialinstallation and to facilitate fast recovery from major disruptions,initially all mesh APs including RAP are on the same (bootstrap)channel. The bootstrap channel may be programmed into all nodes beforeshipping. Alternatively, the bootstrap channel can be determined locallyby having the RAP select one channel and allowing the MAPs to find it.

In an example embodiment, the channel assignment algorithm is acentralized algorithm that leverages the knowledge of the routing treestructure and operates at the controller rather than in each node.During the building of the routing tree, MAPs and the RAP report theirparents, children, and one-hop neighbor lists back to the controller sothat the controller can compile a topology of the mesh network. Notethat the controller knows when the routing tree has been formed (e.g.all or most nodes have registered with the controller).

The following is an algorithm in accordance with an example embodiment:

-   -   1) The controller first assigns two channels to the RAP. The RAP        will use both channels to communicate with its children since it        has no parent to transmit to. The RAP divides its children in        two sets based on the minimization of the cost function and        selects one channel for one set and selects another channel for        the other set.    -   2) The controller examines the nth hop MAPs and assigns channels        to the children of the nth hop MAPs. Note that the cost function        needs to be minimized at every step subject to the first        constraint that the children of the same MAP need to be on the        same channel. Further, all nth hop MAPs in the same collision        domain, i.e. within (k+1)-hop of each other, need to be        considered at each step.    -   3) This repeats for n=2, 3, . . . , until each MAP is assigned a        channel for upstream transmission.    -   4) After the controller assigns the available channels to the        mesh nodes, it instructs the mesh nodes to switch to their        assigned channels.    -   5) In order not to obstruct the normal operation of the whole        mesh network, the channel switching procedure is performed from        the bottom up. It starts from the leaf nodes and stops after all        nodes have switched to their designated channels.

After the network is in operation, channels can be assigned based on thetraffic load on each mesh AP and the percentage of the medium sharedwith external networks. Therefore, in an example embodiment, a goal isto minimize the following cost function:

${{Minimize}\mspace{14mu}{over}\mspace{14mu} c_{j}} \in {C\text{:}\mspace{14mu}{\max\left( {{U\left( {\sum\limits_{i = 1}^{E_{j}}\; u_{i}} \right)} + {\sum\limits_{i = 1}^{N_{j}}\; m_{i}}} \right)}}$Subject  to:  P(noise_floor > T_(f)) < Pfwhere N_(j) is the number of nodes in the same collision domain thatutilize the same channel c_(j)εC to communicate with its parent andE_(j) is the number of external interferers on channel c_(j). m_(i) isthe percentage of medium utilization on channel c_(j) by the ith nodefor transmitting packets and

$U\left( {\sum\limits_{i = 1}^{E_{j}}\; u_{i}} \right)$is the cost of medium utilization level on channel c_(j) by externalinterferers. Both m_(i) and u_(i) are measured by the ith nodeperiodically according to a pre-defined interval. A table look-up can beimplemented to map the percentage of medium busy to the mediumutilization level. The mapping between the percentage of medium busy andthe medium utilization level can be a direct mapping, such as

${U\left( {\sum\limits_{i = 1}^{E_{j}}\; u_{i}} \right)} = {\sum\limits_{i = 1}^{E_{j}}\;{u_{i}.}}$Or U can be adjusted based on the hop count, for example:

Percentage of medium utilized by external Cost of medium interferersutilization level (U ) >60%   1/(1 + hop_count) 60% to 40% 0.6/(1 +hop_count) 40% to 20% 0.4/(1 + hop_count) <20% 0.2/(1 + hop_count)The hop count is considered to ensure that channels chosen by RAP and/orthe 1st-hop MAPs have minimum external interference. The measured noisefloor is used as a constraint. If the measured noise floor for channelc_(j) is over a pre-defined threshold, i.e. T_(f), over a pre-definedpercentage of time, the channel c_(j) is not considered for channelassignment at this AP. This is because even when CCA is not triggered,the noise floor can still be elevated by adjacent channel interferenceand non-WiFi co-channel interference, which adversely affects the meshthroughput. The elevated noise floor can even cause excessive packetlosses since rate shifting can be disabled over the mesh backhaul.

Channel assignment can also be combined with load balancing to furtherimprove network capacity. For instance, if a node experiences frequentbuffer overflows due to high ingress traffic, this node can be eitherassigned a channel with fewer contending nodes or some of its childrencan be moved to different parents by getting different channels from thecurrent parent node.

FIG. 1 illustrates an example of an apparatus 10 configured to implementan example embodiment. Apparatus 10 comprises a transceiver 12configured to be in data communication with an associated mesh networkand channel assignment logic in data communication with the transceiver.“Logic”, as used herein, includes but is not limited to hardware,firmware, software and/or combinations of each to perform a function(s)or an action(s), and/or to cause a function or action from anothercomponent. For example, based on a desired application or need, logicmay include a software controlled microprocessor, discrete logic such asan application specific integrated circuit (ASIC), aprogrammable/programmed logic device, memory device containinginstructions, or the like, or combinational logic embodied in hardware.Logic may also be fully embodied as software.

Transceiver 12 is in data communication with an associated mesh networkvia link 16. Link 16 is suitably any wired or wireless data pathsuitable for acquiring data from the associated mesh network. Inoperation, transceiver 12 can acquire data from the associated meshnetwork that channel assignment logic employs to determine channelassignments. Transceiver 12 is operable to send channel assignments tothe access points.

Referring to FIG. 2, with continued reference to FIG. 1, there isillustrated an example embodiment of a mesh network employing apparatus10 as a controller. In the illustrated embodiment, apparatus 10 iscoupled to root access point 18; however, those skilled in the artshould readily appreciate that in other embodiments apparatus 10 can beco-located with root access point 18 or located anywhere within thenetwork.

Root access point 18 is coupled to three first hop nodes, access points20, 22, 24. The second hop of the network comprises access points 30 and32 coupled to access point 22 and access point 34 coupled to accesspoint 24. A third hop comprises access point 36 that is coupled toaccess point 30.

Channel assignment logic 14 in controller 10 is operable to assignbackhaul channels to each access point 18, 20, 22, 24, 30, 32, 34 and 36of the associated mesh network. Channel assignment logic 14 isconfigured to acquire collision domain data via transceiver 12 for eachaccess point 18, 20, 22, 24, 30, 32, 34 and 36 of the associated meshnetwork.

As will be described in further detail herein, channel assignment logic14 is configured to assign a backhaul channel to each access point 18,20, 22, 24, 30, 32, 34, 36 of the associated mesh network in order tominimize a maximum number of weighted nodes sharing the channel within acollision domain.

In the example embodiment illustrated in FIG. 2, each access point 18,20, 22, 24, 30, 32, 34, 36 has two backhaul radios (not shown). Rootaccess point 18 uses both radios for downlink communications, sincethere are no uplink nodes from root access point 18. Mesh access points20, 22, 24, 30, 32, 34, 36 below root access point 18 employ onebackhaul radio for uplink communications (linked to a parent node with alower hop count) and one backhaul radio for downlink communications(linked to one or more child access points having a higher hop count).For example, mesh access point 22 employs channel 2 as an uplink channelto communicate with root access point 18 and employs channel 4 as adownlink channel to communicate with child access points 30, 32.

At initialization, or at predetermined times or events such as new meshaccess points being detected or a mesh access point is no longeravailable, controller 10 acquires data about the topology of thenetwork. For example controller 10 can request a list comprising aparent access point, children access point and a one-hop neighbor listfrom each access point 18, 20, 22, 24, 30, 32, 34, 36. Channelassignment logic 14 can generate a topology of the mesh network.

Channel assignment logic 14 also acquires data representative of thecollision domain for each of access points 18, 20, 22, 24, 30, 32, 34,36. Any suitable means for determining the collision domain of accesspoints can be employed. For example, each access point may perform11K/RRM exchanges enabling the other access points to determine signalstrengths. Controller 10 can use the signal strength data o predictcollision domains with adequate accuracy. As another example, a linktest run can be run on any individual link and the maximum throughput ofthe individual link test can be recorded. Then simultaneous flows can besent on two links and the combined throughputs of the individual linkscan be compared to the combined throughput. Alternatively, simultaneousflows can be sent on two links and the throughput of the first link withsimultaneous flows can be compared with the throughput of the individualflow to determine whether throughput was affected by the additionalflow.

After the collision domains have been determined, channel assignmentlogic 14 determines channel assignments for access points 18, 20, 22,24, 30, 32, 34, 36. Channel assignment logic 14 assigns a weighted valuefor each channel in the collision domain and attempts to minimize thesum of the weighted nodes sharing the same channel within the samecollision domain. This can be represented as:

${{Minimize}\mspace{14mu}{over}\mspace{14mu} c_{j}} \in {C\text{:}\mspace{20mu}\max\;{\sum\limits_{i = 1}^{\;_{N_{j}}}\; w_{i}}}$where N_(j) is the number of nodes in the same collision domain thatutilize the same channel c_(j)εC to communicate with its parent. w_(i)is the weight assigned to the ith node and it is calculated as the countof the number of nodes on the subtree rooted at the ith node. w_(i) isso defined to take the traffic aggregation factor into consideration.

Controller 10 initially assigns two downlink channels for root accesspoint 18 (e.g. channels 1 and 2). Controller 10 then assigns uplinkchannels for access points 20, 22, 24 to correspond to one of thedownlink channels of root access point 18. Controller 10 then employsthe cost function and assigns downlink channels for the first hop accesspoints, access points 20, 22, 24. This procedure continues until allhops have been assigned backhaul channels. For example, after first hopaccess points have been assigned channels (e.g. access point 20 has nochild access points so it is not assigned a channel, access point 22 isassigned channel 4 and access point 24 is assigned channel 5), the nexthop access points, access points 30, 32 and 34 are assigned channels,and then the final hop access point 36.

In an example embodiment, access points initialize on a predetermined(e.g. bootstrap) channel. This enables controller 10 to communicate withthe access points to acquire data and send channel assignments. Inanother example embodiment, root access point 18 can select one channelfor communicating with the other access points. The other access pointswill scan channels until they locate root access point 18.

Each access point is provided with its channel assignments (uplink anddownlink). Controller 10 can instruct the access points when to switchto their assigned channels. In an example embodiment, channels areswitched starting at the highest hop (e.g. access point 36) andproceeding to the lowest hop until root access point 18 is reached.

Once the network is operated, channel assignments can be adjusted basedon external interference and/or traffic loading. For example, channelassignment logic 14 can be configured to minimize the following costfunction

${{Minimize}\mspace{14mu}{over}\mspace{14mu} c_{j}} \in {C\text{:}\mspace{14mu}{\max\left( {{U\left( {\sum\limits_{i = 1}^{E_{j}}\; u_{i}} \right)} + {\sum\limits_{i = 1}^{N_{j}}\; m_{i}}} \right)}}$Subject  to:  P(noise_floor > T_(f)) < P_(f)where N_(j) is the number of nodes in the same collision domain thatutilize the same channel c_(j)εC to communicate with its parent andE_(j) is the number of external interferers on channel c_(j). m_(i) isthe percentage of medium utilization on channel c_(j) by the ith nodefor transmitting packets and

$U\left( {\sum\limits_{i = 1}^{E_{j}}\; u_{i}} \right)$is the cost of medium utilization level on channel c_(j) by externalinterferers. Both m_(i) and u_(i) are measured by the ith nodeperiodically according to a pre-defined interval. A table look-up can beimplemented to map the percentage of medium busy to the mediumutilization level. The mapping between the percentage of medium busy andthe medium utilization level can be a direct mapping, such as

${U\left( {\sum\limits_{i = 1}^{E_{j}}\; u_{i}} \right)} = {\sum\limits_{i = 1}^{E_{j}}\;{u_{i}.}}$Or U can be adjusted based on the hop count, for example:

Percentage of medium utilized by external Cost of medium interferersutilization level (U ) >60%   1/(1 + hop_count) 60% to 40% 0.6/(1 +hop_count) 40% to 20% 0.4/(1 + hop_count) <20% 0.2/(1 + hop_count)The hop count can be considered to ensure that channels chosen by RAPand/or the 1^(st)-hop MAPs have minimum external interference.

In an example embodiment, the measured noise floor can be used as aconstraint. If the measured noise floor for channel c_(j) is over apre-defined threshold, i.e. T_(f), over a pre-defined percentage oftime, the channel c_(j) is not considered for channel assignment at thisAP. This is because even when CCA is not triggered, the noise floor canstill be elevated by adjacent channel interference and non-WiFico-channel interference, which adversely affects the mesh throughput.The elevated noise floor can even cause excessive packet losses sincerate shifting is disabled over the mesh backhaul.

Channel assignment can also be combined with load balancing to furtherimprove network capacity. For instance, if a node experiences frequentbuffer overflows due to high ingress traffic, this node can be eitherassigned a channel with fewer contending nodes or some of its childrencan be moved to different parents by getting different channels from thecurrent parent node.

FIG. 3 is a block diagram that illustrates a computer system 300 uponwhich an example embodiment may be implemented. For example, computersystem 300 can be employed to implement channel assignment logic 14 inFIG. 1. Computer system 300 includes a bus 302 or other communicationmechanism for communicating information and a processor 304 coupled withbus 302 for processing information. Computer system 300 also includes amain memory 306, such as random access memory (RAM) or other dynamicstorage device coupled to bus 302 for storing information andinstructions to be executed by processor 304. Main memory 306 also maybe used for storing temporary variable or other intermediate informationduring execution of instructions to be executed by processor 304.Computer system 300 further includes a read only memory (ROM) 308 orother static storage device coupled to bus 302 for storing staticinformation and instructions for processor 304. A storage device 310,such as a magnetic disk or optical disk, is provided and coupled to bus302 for storing information and instructions.

An aspect of the example embodiment is related to the use of computersystem 300 for channel assignment for a multi-channel dual radio meshbackhaul. According to an example embodiment, channel assignment for amulti-channel dual radio mesh backhaul is provided by computer system300 in response to processor 304 executing one or more sequences of oneor more instructions contained in main memory 306. Such instructions maybe read into main memory 306 from another computer-readable medium, suchas storage device 310. Execution of the sequence of instructionscontained in main memory 306 causes processor 304 to perform the processsteps described herein. One or more processors in a multi-processingarrangement may also be employed to execute the sequences ofinstructions contained in main memory 306. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions to implement an example embodiment. Thus,embodiments described herein are not limited to any specific combinationof hardware circuitry and software.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 304 forexecution. Such a medium may take many forms, including but not limitedto non-volatile media, volatile media, and transmission media.Non-volatile media include for example optical or magnetic disks, suchas storage device 310. Volatile media include dynamic memory such asmain memory 306. Transmission media include coaxial cables, copper wireand fiber optics, including the wires that comprise bus 302.Transmission media can also take the form of acoustic or light wavessuch as those generated during radio frequency (RF) and infrared (IR)data communications. Common forms of computer-readable media include forexample floppy disk, a flexible disk, hard disk, magnetic cards, papertape, any other physical medium with patterns of holes, a RAM, a PROM,an EPROM, a FLASHPROM, CD, DVD or any other memory chip or cartridge, orany other medium from which a computer can read.

Various forms of computer-readable media may be involved in carrying oneor more sequences of one or more instructions to processor 304 forexecution. For example, the instructions may initially be borne on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 300 canreceive the data on the telephone line and use an infrared transmitterto convert the data to an infrared signal. An infrared detector coupledto bus 302 can receive the data carried in the infrared signal and placethe data on bus 302. Bus 302 carries the data to main memory 306 fromwhich processor 304 retrieves and executes the instructions. Theinstructions received by main memory 306 may optionally be stored onstorage device 310 either before or after execution by processor 304.

Computer system 300 also includes a communication interface 318 coupledto bus 302. Communication interface 318 provides a two-way datacommunication coupling to a network link 320 that is connected to alocal network (not shown), or to a root access point, such as rootaccess point 18 (FIG. 2). For example, communication interface 318 maybe an integrated services digital network (ISDN) card or a modem toprovide a data communication connection to a corresponding type oftelephone line. As another example, communication interface 318 may be alocal area network (LAN) card to provide a data communication connectionto a compatible LAN. Wireless links may also be implemented. In any suchimplementation, communication interface 318 sends and receiveselectrical, electromagnetic, or optical signals that carry digital datastreams representing various types of information. Network link 320typically provides data communication through one or more networks toother data devices.

herein.

In view of the foregoing structural and functional features describedabove, a methodology 400 in accordance with an example embodiment willbe better appreciated with reference to FIG. 4. While, for purposes ofsimplicity of explanation, methodology 400 of FIG. 4 is shown anddescribed as executing serially, it is to be understood and appreciatedthat the example embodiment is not limited by the illustrated order, assome aspects could occur in different orders and/or concurrently withother aspects from that shown and described herein. Moreover, not allillustrated features may be required to implement a methodology inaccordance with an aspect the example embodiment. Embodiments of themethodology are suitably adapted to be implemented in hardware,software, or a combination thereof.

At 402, a collision domain is determined for each mesh access point(MAP). The collision domain may be determined by any suitablymethodology. For example, each mesh access point may broadcast signalsthat can be measured by the other mesh access points. The collisiondomain can be determined based on the measured signal strengths. In anexample embodiment, a first link can be established and a maximumthroughput of the first link is determined. A second link can beestablished and a maximum throughput for the second link is established.Subsequently, the first and second links operate concurrently, the sumof the throughputs of the first and second links can be compared to thesum the individual throughputs. If the sum of the throughputs aresubstantially the same (e.g. within 10-20%), then the two links are notwithin the same collision domain; however, if the sum of the individualthroughputs is higher than the sum of the concurrent throughputs, thenthe links are within the same collision domain.

At 404, the mesh access points initialize on a bootstrap channel. Thebootstrap channel can be a predetermined channel (e.g. can be manuallyprogrammed into the mesh APs). Alternatively, the root access point maybroadcast a signal allowing the other mesh access points to establishcommunications.

At 406, parent, child and 1 hop neighbor lists are acquired for eachaccess point. Each access point determines its parent node, any childnodes and 1 hop neighbors and then transmits the list to the deviceperforming channel assignment (e.g. a controller).

At 408, a tree is generated for the mesh network. The tree starts at theroot access point (RAP) and encompasses descendant access points.

At 410, two channels are assigned to the Root Access Point (RAP). Thechannels can be chosen employing a cost function that minimizes the sumof weighted nodes sharing the same channel within the same collisiondomain. For example, the following cost function can be employed:

${{Minimize}\mspace{14mu}{over}\mspace{14mu} c_{j}} \in {C\text{:}\mspace{14mu}\max{\sum\limits_{i = 1}^{N_{j}}\; w_{i}}}$where N_(j) is the number of nodes in the same collision domain thatutilize the same channel c_(j)εC to communicate with its parent. w_(i)the weight assigned to the ith node and it is calculated as the count ofthe number of nodes on the subtree rooted at the ith node. w_(i) is sodefined to take the traffic aggregation factor into consideration.

At 412, channels are assigned to the remaining hops. After the RAP isassigned, channels are assigned for the first hop and then for each hopof increasing value (e.g. 1, 2, . . . n, where n is the number of thelast hop). The same cost function algorithm described at 410 can beemployed for assigning channels to the remaining hops.

At 414, all of the access points are switched to their assignedchannels. In an example embodiment, channel switching is performed fromthe bottom (e.g. the highest hop count) up (lowest hop count or theRAP).

At 416, after the network is in operation, channels can be assignedbased on the traffic load one each mesh AP and/or the percentage of themedium shared with external networks (or other external interferers). Inan example embodiment, the following cost function can be minimized:

$\max\left( {{U\left( {\sum\limits_{i = 1}^{E_{j}}\; u_{i}} \right)} + {\sum\limits_{i = 1}^{N_{j}}\; m_{i}}} \right)$Minimize  over  c_(j) ∈ C: Subject  to:  P(noise_floor > T_(f)) < P_(f)where N_(j) is the number of nodes in the same collision domain thatutilize the same channel c_(j)εC to communicate with its parent andE_(j) is the number of external interferers on channel c_(j). m_(i) isthe percentage of medium utilization on channel c_(j) by the ith nodefor transmitting packets and

$U\left( {\sum\limits_{i = 1}^{E_{j}}\; u_{i}} \right)$is the cost of medium utilization level on channel c_(j) by externalinterferers. Both m_(i) and u_(i) are measured by the ith nodeperiodically according to a pre-defined interval. A table look-up can beimplemented to map the percentage of medium busy to the mediumutilization level. The mapping between the percentage of medium busy andthe medium utilization level can be a direct mapping, such as

${U\left( {\sum\limits_{i = 1}^{E_{j}}\; u_{i}} \right)} = {\sum\limits_{i = 1}^{E_{j}}\;{u_{i}.}}$Or U can be adjusted based on the hop count:

Percentage of medium utilized by external Cost of medium interferersutilization level (U ) >60%   1/(1 + hop_count) 60% to 40% 0.6/(1 +hop_count) 40% to 20% 0.4/(1 + hop_count) <20% 0.2/(1 + hop_count)The hop count is considered to ensure that channels chosen by RAP and/orthe 1^(st)-hop MAPs have minimum external interference.

The measured noise floor is used as a constraint. If the measured noisefloor for channel c_(j) is over a pre-defined threshold, i.e. T_(f),over a pre-defined percentage of time, the channel c_(j) is notconsidered for channel assignment at this AP. This is because even whenCCA is not triggered, the noise floor can still be elevated by adjacentchannel interference and non-WiFi co-channel interference, whichadversely affects the mesh throughput. The elevated noise floor can evencause excessive packet losses since rate shifting is disabled over themesh backhaul.

Channel assignment can also be combined with load balancing to furtherimprove network capacity. For instance, if a node experiences frequentbuffer overflows due to high ingress traffic, this node can be eitherassigned a channel with fewer contending nodes or some of its childrencan be moved to different parents by getting different channels from thecurrent parent node. At 418, the channel assignments are adjusted. Thecost function can be calculated and channel adjustments implemented atpredetermined intervals are whenever certain events occur such as a newmesh AP is added to the network or communication with a mesh AP is lost.

Described above are example embodiments. It is, of course, not possibleto describe every conceivable combination of components ormethodologies, but one of ordinary skill in the art will recognize thatmany further combinations and permutations of the example embodimentsare possible. Accordingly, this application is intended to embrace allsuch alterations, modifications and variations that fall within thespirit and scope of the appended claims interpreted in accordance withthe breadth to which they are fairly, legally and equitably entitled.

The invention claimed is:
 1. An apparatus, comprising: a transceiverconfigured to be in data communication with an associated mesh network;and channel assignment logic in data communication with the transceiver,the channel assignment logic is operable to assign backhaul channels toeach access point of the associated mesh network; wherein the channelassignment logic is configured to acquire collision domain data for eachaccess point of the associated mesh network wherein a collision domainis defined as a node's (k+1) hop neighborhood, where k is a ratiobetween a carrier sense range and a communication range; wherein thechannel assignment logic is configured to assign a backhaul channel toeach access point of the associated mesh network in order to minimize amaximum number of access points sharing the channel within a collisiondomain; wherein the channel assignment logic determines the carriersense range for each selected access point in accordance with a transmitpower of the selected access point, a path loss through the selectedaccess point, and a sensitivity of a receiver of the selected accesspoint at a lowest selected data rate; and wherein the channel assignmentlogic determines the communication range for each selected access pointin accordance with a transmit power of the selected access point, a pathloss through the selected access point, and a sensitivity of thereceiver of the selected access point operated at a predetermineddesired data rate.
 2. The apparatus of claim 1, further comprising: thechannel assignment logic is configured to acquire parent, children and aone-hop neighbor list for each access point of the associated meshnetwork; and the channel assignment logic is configured to generate atopology of the mesh network.
 3. The apparatus of claim 1, wherein thechannel assignment logic is configured to acquire collision domain databy instructing each access point to transmit a signal and acquiringreceived signal strength data from access points receiving the signal.4. The apparatus of claim 1, wherein the channel domain logic isconfigured to acquire collision domain data by performing an individuallink test on a first link and acquiring a maximum throughput; whereinthe channel domain logic is further configured to perform a multiplelink test on the first link and a second link and determining a maximumthroughput for the first link while testing the second link; and whereinthe channel domain logic is further configured to determine the secondlink is within the collision domain of the first link responsive todetermining the maximum throughput for the multiple link test is lowerthan the maximum throughput for the individual link test.
 5. Theapparatus of claim 1, wherein the access points on the associatednetwork initialize to a predetermined channel; and the channelassignment logic is further configured to signal the access points toswitch to their assigned channels.
 6. The apparatus of claim 1, furthercomprising: the channel assignment logic is configured to acquire datarepresentative of external interference for each access point of theassociated network; and the channel assignment logic is configured toadjust channel assignments based on external interference.
 7. Theapparatus of claim 6, wherein the channel assignment logic is furtherconfigured to adjust the external interference data based on hop countso that access points with lower hop counts are assigned channels withlower interference.
 8. The apparatus of claim 7, further comprising: thechannel assignment logic is configured to acquire data representative ofmedia utilization for each access point of the associated network; andthe channel assignment logic is configured to adjust channel assignmentsbased on media utilization.
 9. The apparatus of claim 1, furthercomprising: the channel assignment logic is configured to acquire datarepresentative of external interference for each access point of theassociated network; the channel assignment logic is configured toacquire data representative of media utilization for each access pointof the associated network; and the channel assignment logic isconfigured to adjust channel assignments to minimize the sum of externalinterference and media utilization for each channel.
 10. The apparatusof claim 1, wherein the channel assignment logic is further configuredto acquire data representative of a noise floor for each channel,wherein the channel assignment logic is configured to not assign achannel to an access point responsive to the noise floor being above apredetermined level for a predetermined amount of time.
 11. A method,comprising: acquiring collision domain data for each access point of anassociated mesh network, wherein each access point is configured with atleast first and second wireless transceivers for communicating on firstand second channels respectively wherein a collision domain is definedas a node's (k+1)-hop neighborhood, where k is a ratio between a carriersense range and a communication range; calculating a cost function foreach access point of the associated mesh network, the cost functionassigning a weighted value for each access point in a collision domainbased on a number of access points in the collision domain; andselecting channel assignments for each access point that minimizes thecost function; wherein the carrier sense range is determined for eachselected access point in accordance with a transmit power of theselected access point, a path loss through the selected access point,and a sensitivity of a receiver of the selected access point at a lowestselected data rate; and wherein the communication range is determinedfor each selected access point in accordance with a transmit power ofthe selected access point, a path loss through the selected accesspoint, and a sensitivity of the receiver of the selected access pointoperated at a predetermined desired data rate.
 12. The method of claim11, wherein each access point is assigned a weighting value is based ona number of sub-tree nodes rooted at the weighted node; and whereinselecting the channel assignments for each access point minimizes amaximum number of access points having the same weighting value sharingthe same channel within a collision domain.
 13. The method of claim 11,the selecting channel assignments further comprises: selecting twodownlink channels for the root access point; selecting an uplink channelfor each access point at each hop to match a downlink channel of aparent access point; and selecting downlink channels for each accesspoint at each hop that minimize the cost function; and repeatingselecting an uplink channel and selecting downlink channels for eachhop, wherein each iteration is a higher hop.
 14. The method of claim 11,further comprising: acquiring data representative of externalinterference for each access point of the associated mesh network; andadjusting backhaul channel assignments based on external interference.15. The method of claim 14, the adjusting backhaul channel assignmentsfurther comprises assigning a priority value inverse to hop count. 16.The method of claim 11, further comprising: acquiring datarepresentative of media utilization for each access point of theassociated mesh network; and adjusting channel assignments based onmedia utilization for each access point.
 17. An apparatus, comprising: atransceiver in operative communication with an associated first accesspoint and with an associated second access point; channel assignmentlogic that sends and receives data via the transceiver; wherein thechannel assignment logic obtains data representative of a first maximumthroughput from the associated first access point via the transceiver,wherein the first maximum throughput is determined while the firstaccess point is transmitting and an associated second access point isnot transmitting; wherein the channel assignment logic obtains datarepresentative of a second maximum throughput from the second accesspoint via the transceiver, wherein the second maximum throughput isdetermined while the second access point is transmitting and the firstaccess point is not transmitting; wherein the channel assignment logicobtains data representative of a third maximum throughput from the firstaccess point via the transceiver, wherein the third maximum throughputis determined while the first and second access points are transmitting;wherein the channel assignment logic obtains data representative of afourth maximum throughput from the second access point via thetransceiver, wherein the fourth maximum throughput is determined whilethe first and second access points are transmitting; wherein the channelassignment logic determines a first sum of the first maximum throughputand second maximum throughput; wherein the channel assignment logicdetermines a second sum of the third maximum throughput and the fourthmaximum throughput; and wherein the channel assignment logic determineswhether the associated first access point and the associated secondaccess point are in the same collision domain in accordance with asimilarity between the first sum and the second sum.
 18. The apparatusof claim 17, wherein the channel assignment logic obtains datarepresentative of a fifth maximum throughput from an associated thirdaccess point via the transceiver, wherein the fifth maximum throughputis determined while the third access point is transmitting and the firstaccess point is not transmitting; wherein the channel assignment logicobtains data representative of a sixth maximum throughput from theassociated third access point via the transceiver, wherein the sixthmaximum throughput is determined while the associated first and thirdaccess points are transmitting; and wherein the channel assignment logicdetermines the associated first access point and the associated thirdaccess point are in the same collision domain responsive to determininga sum of the first maximum throughput and third maximum throughput isnot similar to a sum of the fifth maximum throughput and the sixthmaximum throughput.
 19. The apparatus of claim 18, wherein the channelassignment logic determines the associated first access point and thirdaccess point are in the same collision domain responsive to determininga sum of the first maximum throughput and third maximum throughput isnot similar to a sum of the fifth maximum throughput and the sixthmaximum throughput and the sum of the first maximum throughput and thirdmaximum throughput is greater than the sum of the fifth maximumthroughput and sixth maximum throughput.
 20. The apparatus of claim 17,wherein the channel assignment logic determines the sum of the firstmaximum throughput and second maximum throughput is similar to the sumof the third maximum throughput and the fourth maximum throughputresponsive to the sum of the first maximum throughput and second maximumthroughput being within twenty percent of the sum of the third maximumthroughput and the fourth maximum throughput.
 21. The apparatus of claim1, wherein: the channel assignment logic is configured to assign abackhaul channel to each access point of the associated mesh network inorder to minimize a maximum number of access points sharing the channelwithin a collision domain according to:Minimize over c_(j)εC:maxΣ_(i=1) ^(N) ^(j) w_(i) wherein N_(j) is thenumber of nodes in the same collision domain that utilize the samechannel c_(j)εC to communicate with its parent; w_(i) is the weightassigned to the i^(th) node and it is calculated as the count of thenumber of nodes on the subtree rooted at the i^(th) node, wherein w_(i)is so defined to take the traffic aggregation factor into consideration.